Conventionally, if a specific internal pressure is desired in a cavity of a micromechanical component or if a gas mixture having a specific chemical composition is to be sealed inside the cavity, then the internal pressure or the chemical composition is frequently adjusted when encapsulating the micromechanical component or during the bonding process between a substrate wafer and a cap wafer. During the encapsulation, a cap is joined to a substrate, for instance, whereby the cap and the substrate jointly enclose the cavity. Adjusting the atmosphere or the pressure and/or the chemical composition of the gas mixture prevailing in the environment during the encapsulation therefore allows for an adjustment of the specific internal pressure and/or the specific chemical composition in the cavity.
Micromechanical components such as inertial sensors are preferably hermetically sealed by a wafer bonding process in order to protect the sensors from environmental influences (dust, moisture, gas) or to selectively enclose certain gases or a vacuum. Examples of methods for the hermetical sealing of micromechanical inertial sensors at the wafer level are eutectic bonding, glass-frit bonding and thermo-compression bonding.
Currently, a defined pressure (e.g., a vacuum around 1 mbar, a medium pressure around a few 100 mbar or an overpressure up to 2000 mbar) or a specific gas (e.g., nitrogen or neon) is adjusted. In general, a low internal pressure is adjusted in yaw-rate sensors (high-quality systems) and a high internal pressure is adjusted in the case of acceleration sensors (high damping), which is achieved by an evacuation or by the selective supply of a gas during the wafer-bonding process.